Methods of producing concentrated urea-sulfuric acid reaction products

Abstract

Stable concentrated solutions of urea and sulfuric acid containing mono- and/or diurea sulfates and less than 35 weight percent water, free of sulfamic acid and/or ammonium sulfamate, are produced by a unique process that involves the simultaneous and separate addition of urea, sulfuric acid and optionally water to a reaction zone at controlled rates and in stochiometric proportions equivalent to the composition of the desired product, and maintaining reaction temperatures below the incipient decomposition temperature for the particular composition. The heat generated by the highly exothermic reaction can be removed by cooling the liquid phase during the course of the reaction by direct air heat exchange with only nominal, if any, atmospheric emissions.

I claim: 
     
       1. A method for producing concentrated solutions of urea and sulfuric acid of predetermined composition which method comprises the steps of: (i) simultaneously adding urea, concentrated sulfuric acid, and optionally water to a reaction zone at relative rates corresponding to the concentration of each respective component in said predetermined composition and within the ranges of about 5 to about 75 weight percent urea, about 5 to 85 weight percent sulfuric acid, and 0 to about 35 weight percent water, in which said urea and sulfuric acid are introduced to said reaction zone separately of each other and, in combination, constitute at least about 65 weight percent of the feed to the reaction zone, (ii) continuously agitating said reacting liquid phase formed by the addition of said urea, sulfuric acid, and water to said reaction zone during the addition of said urea, acid and water to rapidly disperse said urea, acid, and water therein, (iii) cooling said reacting liquid phase during the addition of said urea, acid and water by an amount sufficient to maintain said liquid phase at a temperature of about 176°  F. or less and below the incipient decomposition temperature of said predetermined composition, and (iv) recovering from said reaction zone a product solution having said predetermined composition. 
     
     
       2. The method defined in claim 1 wherein (i) said urea, sulfuric acid and water added to said reaction zone are admixed therein with said reacting liquid phase comprising urea, acid, water and reaction product of said predetermined composition, (ii) the quantity of said reacting liquid phase in said reaction zone corresponds to at least about 0.1 times the combined hourly addition rates of said urea, sulfuric acid and water, and (iii) said liquid phase is maintained at a temperature of at least about 120° F. 
     
     
       3. The method defined in claim 2 wherein said urea, sulfuric acid and water are simultaneously added to said reaction zone at rates corresponding to about 10 to about 70 weight percent urea, about 10 to about 80 weight percent sulfuric acid, and about 0 to about 25 weight percent water, the combined weights of sulfuric acid and urea added to said reaction zone correspond to at least about 75 weight percent of the total feed to said reaction zone; and said reacting liquid phase is continuously cooled during the addition of said urea, sulfuric acid and water by an amount sufficient to maintain a temperature of about 170° F. or less. 
     
     
       4. The method defined in claim 2 wherein said predetermined composition has a crystallization temperature of about 77° F. or less and a composition falling on or above the 77° F. isotherm of the ternary phase diagram of FIG. 1, and said reacting liquid phase is maintained at a temperature of about 160° F. or less. 
     
     
       5. The method defined in claim 2 wherein said predetermined composition contains, and the respective feed rates to said reaction zone comprise, 0 to 15 weight percent water and at least about 85 weight percent urea and sulfuric acid taken in combination. 
     
     
       6. The method defined in claim 2 wherein said predetermined composition comprises, and the respective feed rates to said reaction zone correspond to, about 0 to about 25 weight percent water and at least about 75 weight percent urea and sulfuric acid taken in combination, and the weight ratio of sulfuric acid to urea in said predetermined composition and in said feed to said reaction zone is at least about 1. 
     
     
       7. The method defined in claim 2 wherein said reacting liquid phase is maintained at a temperature of about 150° F., or less, and said product solution contains less than about 0.1 weight percent of a member selected from the group consisting of sulfamic acid, ammonium sulfamate and combinations thereof. 
     
     
       8. The method defined in claim 2 wherein said reaction zone comprises at least one reaction vessel and cooling means external of said reaction vessel, and wherein said method further comprises the steps of simultaneously adding said urea, sulfuric acid and water to said reaction vessel and admixing the same with said reacting liquid phase of urea, acid, water and reaction product of said predetermined composition within said reaction zone, circulating at least a portion of said reacting liquid phase from said reaction vessel through said cooling means to cool the same, and returning at least a portion of the cooled reacting liquid phase to said reaction vessel. 
     
     
       9. The method defined in claim 8 wherein said cooling means comprises a direct contact countercurrent air heat exchanger, and said method further comprises the steps of passing hot reacting liquid phase from said reaction vessel downwardly through said heat exchanger, passing air upwardly through said heat exchanger into direct heat exchange contact with said liquid phase and cooling said liquid phase, returning at least a portion of the resulting cooled liquid phase to said reaction vessel, and discharging said air from said heat exchanger to the atmosphere. 
     
     
       10. The method defined in claim 9 wherein said urea, sulfuric acid and water are continuously added simultaneously to said reaction vessel at a combined rate equivalent to a predetermined production rate, product solution of said predetermined composition is continuously removed from said reaction zone at said predetermined production rate, and the volume of said reacting liquid phase in said reaction zone corresponds to at least said predetermined production rate. 
     
     
       11. The method defined in claim 10 which further comprises determining (i) the amount of water removed from said liquid phase in said heat exchanger and (ii) the concentration of urea, sulfuric acid and water in a member selected from the group consisting of said liquid phase, said product solution, and combinations thereof, and adjusting the urea, sulfuric acid and/or water feed rates to said reaction vessel responsive to the determinations of items (i) and (ii) as required to maintain the composition of said product solution at said predetermined composition. 
     
     
       12. The method defined in claim 2 wherein said urea, sulfuric acid and water are continuously added simultaneously to said reaction vessel at a combined rate equivalent to a predetermined production rate, product solution of said predetermined composition is continually removed from said reaction zone at said predetermined production rate, and the volume of said reaction liquid phase in said reaction zone corresponds at least to the value of V o  determined in accordance with the expression V o  =k/u(14.3 d 2  -1) wherein k is the first order rate constant for said predetermined product in reciprocal minutes, d is the diameter of the largest urea feed particles in millimeters, V o  is the volume of said reaction liquid phase within said reaction zone in gallons, and u is the production rate from the reaction zone in gallons per minute. 
     
     
       13. The method defined in claim 1 wherein said urea, sulfuric acid and water are continuously added simultaneously to said reaction vessel at a combined rate equivalent to a predetermined production rate, product solution of said predetermined composition is continuously removed from said reaction zone at said predetermined production rate, and the volume of said reacting liquid phase in said reaction zone corresponds to at least about one-half said predetermined production rate. 
     
     
       14. The method defined in claim 13 wherein said predetermined composition has a predetermined crystallization temperature of about 80° or less, and the feed rates of said urea, sulfuric acid and water to said reaction vessel are continuously controlled within predetermined limits sufficient to maintain the concentration of each of said urea, sulfuric acid and water in said product solution within 2 weight percent of their predetermined concentrations and to maintain the crystallization temperature of said product solution within 10° F. of said predetermined crystallization temperature. 
     
     
       15. The method defined in claim 1 wherein the weight ratio of said sulfuric acid to said urea in said product solution is at least about one, said product solution comprises 0 to about 25 weight percent water, said urea and said sulfuric acid, in combination, constitute at least about 75 weight percent of said product solution, and said product solution is free of reaction by-products resulting from the decomposition of a member selected from the group consisting of said urea, said sulfuric acid, and combinations thereof. 
     
     
       16. The method defined i claim 1 wherein said cooling of said reacting liquid phase during the addition of said urea, acid and water, is achieved, at least in part, by directly contacting said reacting liquid phase with air. 
     
     
       17. A method for continuously producing concentrated, stable solutions of urea and sulfuric acid of predetermined composition which method comprises the steps of (i) continuously and simultaneously adding urea, sulfuric acid and water to a reacting liquid phase, hereinafter defined, in a reaction zone at relative rates corresponding to the concentration of each respective component in said predetermined composition and within the ranges of about 5 to about 75 weight percent urea, about 5 to 85 weight percent sulfuric acid, and 0 to about 35 weight percent water, in which said urea and sulfuric acid constitute at least about 65 weight percent of the feed to said reaction zone and are added separately to said reaction zone, (ii) admixing said urea, sulfuric acid and water in said reaction zone with a reacting liquid phase comprising urea, sulfuric acid, water and said reaction product of said predetermined composition, the quantity of said reacting liquid phase in said reaction zone corresponding to at least about one half the combined hourly addition rates of said urea, acid and water to said reaction zone and being sufficient to prevent the discharge of unreacted urea in the product from said reaction zone, (iii) agitating said reacting liquid phase continuously during the addition of said urea, sulfuric acid and water to rapidly disperse the same therein, (iv) cooling at least a portion of said reacting liquid phase by an amount sufficient to maintain the temperature of said reacting liquid phase at a level of about 120° F. to about 176° F., and below the incipient decomposition temperature of said predetermined composition, and (v) continuously withdrawing product solution of said predetermined composition from said reaction zone. 
     
     
       18. The method defined in claim 17 wherin (i) said urea is selected from the group consisting of prilled urea and granular urea, and combinations thereof, (ii) the volume of said reacting liquid phase in said reaction zone corresponds to at least about said combined hourly addition rate of said urea, sulfuric acid and water, (iii) said reacting liquid phase is maintained at a temperature below about 170° F., (iv) said concentrations of said urea, sulfuric acid and water in said predetermined composition are within the ranges of about 10 to about 70 weight percent urea, about 10 to about 80 percent sulfuric acid and about 0 to about 25 weight percent water, and (v) said urea and sulfuric acid constitute at least about 75 weight percent of said predetermined composition. 
     
     
       19. A composition of matter comprising about 5 to about 75 weight percent urea, about 5 to about 85 weight percent sulfuric acid, and about 0 to 35 weight percent water based on the combined weight of urea, sulfuric acid and water, and less than about 0.1 weight percent of a member selected from the group consisting of sulfamic acid, ammonium sulfamate, and combinations thereof, in which at least a portion of said urea and sulfuric acid are present as a member selected from the group consisting of monourea sulfate, diurea sulfate, and combinations thereof. 
     
     
       20. The composition defined in claim 19 comprising about 10 to about 70 weight percent urea, about 10 to about 80 weight percent sulfuric acid, and about 0 to about 25 weight percent water, wherein the weight ratio of sulfuric acid to urea is at least about 1. 
     
     
       21. The composition defined in claim 20 containing no detectable amount of a member selected from the group consisting of sulfamic acid, ammonium sulfamate and combinations thereof. 
     
     
       22. The composition defined in claim 19 containing less than about 0.05 weight percent of said member selected from the group consisting of sulfamic acid, ammonium sulfamate, and combinations thereof. 
     
     
       23. The composition defined in claim 19 containing no detectable amount of a member selected from the group consisting of sulfamic acid, ammonium sulfamate and combinations thereof. 
     
     
       24. The method of improving the quality of agricultural soils including the steps of applying to said soil an agronomically effective amount of the composition defined in claim 23. 
     
     
       25. The method of fertilizing crops including the steps of applying to said crop an agronomically effective amount of the composition defined in claim 23. 
     
     
       26. The method defined in claim 25 wherein said composition is applied to said crop at a rate equivalent to a nitrogen dosage of at least about 40 lbs. of nitrogen per acre of said crop. 
     
     
       27. A method for producing concentrated solutions of urea and sulfuric acid of predetermined composition, which method comprises the steps of: (i) simultaneously adding urea, concentrated sulfuric acid, and optionally water, to a reaction zone at relative rates corresponding to the concentration of each respective component in said predetermined composition, and within the ranges of about 10 to about 70 weight percent urea, about 10 to about 80 weight percent sulfuric acid, and 0 to about 35 weight percent water, in which said urea and said sulfuric acid, in combination, constitute at least about 65 weight percent of the feed to said reaction zone and are introduced into said reaction zone separately of each other, and in which the weight ratio of said sulfuric acid to said urea is at least about 1, (ii) continuously agitating the resulting liquid phase in said reaction zone during the addition of said urea, acid, and optionally water, to rapidly disperse said urea, acid, and water therein, (iii) cooling said liquid phase during said addition of said urea, acid, and water, by an amount sufficient to maintain said liquid phase at a temperature of about 176° F. or less, and below the incipient decomposition temperature of said predetermined composition, and (iv) recovering from said reaction zone a product solution having said predetermined composition free of reaction byproducts resulting from the decomposition of a member selected from the group consisting of urea, sulfuric acid, and combinations thereof. 
     
     
       28. The method defined in claim 27 wherein said product solution comprises 0 to about 25 weight percent water, said urea and said sulfuric acid, in combination, constitute at least about 75 weight percent of said product solution, and said product solution is free of reaction by-products resulting from the decomposition of said urea. 
     
     
       29. A composition of matter comprising the reaction product of urea and sulfuric acid, which composition contains 0 to about 35 weight percent water, about 10 to about 80 weight percent sulfuric acid, and about 10 to about 70 weight percent urea, wherein said urea and said sulfuric acid, in combination, constitute at least about 65 weight percent of said composition, the weight ratio of said sulfuric acid to said urea is at least about one, and wherein said composition is free of urea-sulfuric acid reaction by-products resulting from the decomposition of a member selected from the group consisting of urea, sulfuric acid, and combinations thereof. 
     
     
       30. The composition defined in claim 29 comprising 0 to about 25 weight percent water, wherein said urea and said sulfuric acid, in combination, constitute at least about 75 weight percent of said composition, and said composition is free of reaction by-products resulting from the decomposition of said urea. 
     
     
       31. A composition of matter comprising the reaction product of urea and sulfuric acid, about 10 to about 80 weight percent sulfuric acid, and which composition contains 0 to about 35 weight percent water, about 10 to about 70 weight percent urea, wherein said urea and said sulfuric acid, in combination, constitute at least about 65 weight percent of said composition, and wherein said composition is free of urea-sulfuric acid reaction by-products resulting from the decomposition of a member selected from the group consisting of urea, sulfuric acid and combinations thereof. 
     
     
       32. The composition defined in claim 31 comprising 0 to about 25 weight percent water, wherein said urea and said sulfuric acid, in combination, constitute at least about 75 weight percent of said composition, and said composition is free of reaction by-products resulting from the decomposition of said urea. 
     
     
       33. The method defined in claim 1 wherein said product solution recovered from said reaction zone is free of decomposition products of urea, sulfuric acid, and combinations therof formed by the reaction of said urea and said sulfuric acid in said reactio zone. 
     
     
       34. A composition of matter formed by the reaction of urea and sulfuric acid to convert at least a portion of said urea and sulfuric acid to a member selected from the group consisting of the monourea adduct of sulfuric acid, the diurea adduct of sulfuric acid, and combinations thereof, which composition comprises 0 to about 35 weight percent water, about 10 to about 80 weight percent sulfuric acid, and about 10 to about 70 weight percent urea, wherein said urea and sulfuric acid, in combination, constitute at least about 65 weight percent of said composition, and wherein said composition is free of decomposition products of urea, sulfuric acid, and combinations thereof, formed by said reaction of said urea and sulfuric acid. 
     
     
       35. The composition of matter produced by the method which comprises the steps of reacting urea, sulfuric acid, and optionally water, in proportions within the ranges of about 10 to about 70 weight percent urea, about 10 to about 80 weight percent sulfuric acid, and 0 to about 35 weight percent water, in which said urea and said sulfuric acid, in combination, constitute at least about 65 weight percent of the combination of said urea, sulfuric acid, and water, and maintaining the temperature of said combination of said urea, sulfuric acid and water below its incipient decomposition temperature. 
     
     
       36. The composition defined in claim 35 wherein the temperature of said combination of said urea, sulfuric acid, and water, is maintained below 176° F. 
     
     
       37. The method defined in claim 35 wherein the temperature of said combination of said urea, sulfuric acid, and water, is maintained below about 160° F. 
     
     
       38. The composition defined in claim 35 wherein the temperature of said combination of said urea, sulfuric acid, and water, is maintained below about 155° F., and the weight ratio of said urea to said sulfuric acid is at least about 1. 
     
     
       39. A method for producing reaction products of urea and sulfuric acid, which method comprises the steps of combining urea, sulfuric acid, and optionally water, in proportions corresponding to about 10 to about 70 weight percent urea, about 10 to about 80 weight percent sulfuric acid, and 0 to about 35 weight percent water, wherein said urea and said sulfuric acid, in combination, constitute at least about 65 weight percent of said reaction product, reacting said urea with said sulfuric acid in said combination to produce said reaction products, and, at all times during said reaction, maintaining the temperature of said combination at a level below the incipient decomposition temperature of said combination. 
     
     
       40. The method defined in claim 39 wherein said temperature of said combination is maintained at a level below about 176° F. 
     
     
       41. The method defined in claim 39 wherein said temperature of said combination is, at all times during reaction, maintained at a temperature below about 160° F. 
     
     
       42. The method defined in claim 39 wherein said temperature is maintained at a level of about 155° F. or less and the weight ratio of said urea to said sulfuric acid in said combination is at least about 1. 
     
     
       43. The method of improving the quality of agricultural soils including the step of applying to said soil an agronomically effective amount of the composition defined in claim 29. 
     
     
       44. The method of fertilizing crops including the step of applying to said crop an agronomically effective amount of the composition defined in claim 29. 
     
     
       45. The method of improving the quality of agricultural soils including the step of applying to said soil an agronomically effective amount of the composition defined in claim 31. 
     
     
       46. The method of fertilizing crops including the step of applying to said crop an agronomically effective amount of the composition defined in claim 31. 
     
     
       47. The method of improving the quality of agricultural soils including the step of applying to said soil an agronomically effective amount of the composition defined in claim 34. 
     
     
       48. The mehtod of fertilizing crops including the step of applying to said crop an agronomically effective amount of the composition defined in claim 34. 
     
     
       49. The method of improving the quality of agricultural soils including the step of applying to said soil an agronomically effective amount of the composition defined in claim 35. 
     
     
       50. The method of fertilizing crops including the step of applying to said crop an agronomically effective amount of the composition defined in claim 35. 
     
     
       51. The method of improving the quality of agricultural soils including the step of applying to said soil an agronomically effective amount of the composition defined in claim 36. 
     
     
       52. The method of fertilizing crops including the step of applying to said crop an agronomically effective amount of the composition defined in claim 36.